Man and many other organisms possess internal cellular mechanisms which are manifested as daily (circadian) rhythms. Biological rhymicity is of importance with regard to the fundamental cellular processes responsible and how they may relate to cell cycles and cell proliferation. In both psychiatry and medicine it is known that circadian rhythmicity is involved in the timing of bodily functions, work-rest cycles, jet lag, sleep, drug tolerance and drug efficacy. This research program is concerned with the elucidation of the basic cellular and molecular mechanisms involved in circadian rhythmicity. Our studies will utilize the unicellular dinoflagellate, Gonyaulax, and we will carry out studies designed to elucidate the fundamental molecular and cellular mechanisms responsible. To this end we will examine the effects of drugs and inhibitors on the phase and period of the rhythm in an effort to pinpoint key metabolic pathways. Most important will be to identify the actual effects of effective drugs (such as protein synthesis inhibitors). Secondly, we will be to identify the actual effects of effective drugs (such as protein synthesis inhibitors). Secondly, we will compare rhythms of bioluminescence with time of cell division and time of key molecular events associated with the cell cycle both in cultures and in single isolated cells. In this work we will attempt to find out if, when circadian cells are dividing slowly, they nevertheless experience multiple fundamental cell cycle rounds. We will also continue to study enzymes whose activities are controlled by the circadian mechanism. We will also make a study of cell volumes and water content as a function of time of day and environmental conditions. This study will focus on whether there is a large uptake of cell water, coincident with the end of S-phase, that causes the glow. Osmotic manipulations of cell water and thus size will be performed, and correlated with individual cell luminescent response. Fractionation of the cell population into size classes by sieving on electron microscope grids will be done to correlate cell size, and age after division, with circadian parameters as measured by luminescence. Simultaneously, computer modeling of the time course of cell growth will be carried out based on a model (Krasnow 1978), and the model will be tested against the experimental data.